This invention relates to optical assemblies for color television including color splitting prisms and solid-state imagers.
Monochrome television cameras previously used vacuum camera tubes as transducers for generating a sequential electrical signal representative of the brightness of a scene by line-scanning the photosensitive surface of the camera tube. The image of a scene to be televised was focused on the photosensitive surface by a lens system. With the advent of color television, means were required to produce signals representative of the various colors of the scene being televised. One way in which color-representative signals could be generated would be to fit each of three cameras with appropriate color filters and focus each one through its own individual lens onto a scene to be televised. Such an arrangement, however, requires three lenses, and views the scene from three different locations, thereby producing parallax error. Additionally, three separate cameras are difficult to maintain in registration except on a stationary basis.
Another way of generating color television signals is by the use as transducers of three camera tubes, each viewing the scene to be televised through an individual color filter and all three being optically multiplexed through a common lens system by means of a light-splitting arrangement. In such an arrangement, the requirement for a multiplicity of lenses is avoided and parallax error is eliminated, and the registration problem is solved by adjusting the position of each camera tube relative to the exit port of the light-splitting assembly to which it is optically coupled. Thus, by viewing the scene on a monitor by way of one of the camera tubes such as the green camera tube, the red camera tube image can be superimposed electrically on the green image, and the red tube can be adjusted relative to the light-splitting arrangement so as to exactly superimpose or register the images being viewed. The blue camera tube is then manipulated so as to superimpose the blue component of the image as viewed on the monitor with the registered green and red images. The manipulators are then locked in the position which gives the best registration.
In recent years, a great deal of attention has been directed toward solid-state imagers such as charge-coupled imagers. These imagers have the advantages of discrete light-sensing areas which can be addressed either individually or in groups, small size, light weight, and they have no inherent degradation mechanism to cause early failure. However, the solid-state imagers have disadvantages in that they are subject to inherent defects which occur during manufacture, the design and packaging are not standardized, and complex electronics may be required for their control. It is desirable to eliminate the bulk and weight of prior art cameras, improve reliability and reduce maintenance.